Plastic film or sheet containing cellulose nitrate



Patented] 15, 1931 j UNl-TED STATES PATENT OFFICE mime E'jwALsn, 0E EASTORANGE, AND THOMAS E. ALCORN, '0]? MA'rLEwoon, NEW

JERSEY, nssrenoas TO cE LUEoIn coaromrron, A coaroannon 0E NEW JERSEYrms'rrc mm on SHEET con'mmiie cELLuLosE nirnarn Ho Drawing.

This invention relates to the reparation of films or sheets containingcelliilose nitrate and relates more particularly to the use of cellulosenitrate of comparatively low nitrogen content and of low viscositycharacteristics in the preparation of films or sheets.

An object of our invention is to prepare films or sheets containingcellulose nitrate of low viscosity characteristics, and preferably ofrelatively low nitrogen content whereby films or sheets may be producedwhich have properties that are superior to those found in sheets orfilmsheretofore made. Other objects of our, invention will appear from thefollowing detailed description.

Heretofore cellulose nitrate films have been prepared by spreading orflowing viscous solutions of the same onto metallic or other surfaces,and after suitable exposure to cause evaporation of the volatilesolvents, the dry or partially dry film was stripped for use or othertreatment. i

. However in this process, it has been necessary'. to employ a cellulosenitrate or pyroxylin of about 12% nitrogen content produced by'thereaction of a mixture of sulphuric acid and nitric acid on cellulose,without further treatment to alter the viscosity or solubilitycharacteristics of the cellulose nitrate after such nitration. Filmsformed in this manner have been limited in Ino their commercialapplication because of their lack of plasticity under heat andtheir'sluggish res onse to c'gmenting operations.

er to overcome the diificulties when such cellulose nitrate wasempolyed, it has been necessary to use'large proportions of camphor orequivalent plastifiers-and' also certain modifiers such as fusel oil orsimilar-high boilers,all of which tended to distort the films'or toimpart to them an undesirable degree of softness.

'We have discovered. hat all ficulties encountered in making a plasticfilm containing cellulose nitrate may be obviated by the use of acellulosenitrate or pyroxylin of lower nitrogen content and of lowerviscosity. 1

- In accordance with our invention, we pre-v pare films or sheets fromsolutions of celluface and are of the viscosity .Applicaticin filedNovember 24, 1928. Serial No. 321,759.

lose mtrate or pyroxylm of a comparatlvely low degree of nitration andhaving low viscosity characteristics, preferably lowering this viscosityby chemical and/or physical as is used for forming films, and thevolatile means of a heated atmosphere. Theamount of solution flowedonto-the surface is such solvent is caused to evaporate preferably bythat itproduces fihns or sheets ranging in thickness from that ofordinary films to. that of the comparatively thick sheets whichheretofore have been made by cutting from blocks of plastic masses ofcellulose nitrate. The films are then stripped from the surgiven anysubsequent treatment desired.

. Therellulose nitrate or pyroxylin to be employed in our process ispreferably one that has a nitrogen content of 10.7 to 11.35%- andpreferably 11%. The viscosity characteristics of the cellulose nitrateemployed is preferably from 10' to 7 5 seconds. ;Th1s viscosity isdetermined by measuring the time required for a steel ball having adiameter of3/32 of an inch to fall the distance of 11.44

inches through a solution maintained at a temperature of 25 (1, which[solution is formed by dissolving one part of the cellulose'nitrate in 9parts of a mixture'of equal 'weights'of 188 proof ethyl alcohol andacetone. This low viscosity cellulose nitrate may be made in anysuitable manner known to the pyroxylin art; However we prefer to prepareit by treating a cellulose nitrate after it has been formed bynitration'of. cellulose of these .dif-

with hot water under pressure in the presence of or the absence ofchemical agents such as catalysts that promote the reductioncharacteristics ofythe cellulose nitrate.

Any suitable volatile solvent may be employed inmaking the solution,examples of which' are acetone, a mixture ofethyl alcohol if or methylalcohol with ether, or a mixture of ethyl alcohol or methyl alcohol withacetone.

.While we prefer to employ camphor as the to the surfaces, which werenot intended to be removed from such surfaces. Moreover even if suchfilms were to be detached from the surfaces to which they are applied,

plastifier, other suitable plastifiers such as dithey would be found tobe very brittle, and ethyl phthalate or dibutyl phthalate may beemployed. The amount of plastifier used is generally within the range ofthat'employed for making sheets from plastic compositions. As an exampleof the quantity ,of plastifier that is suitable, it is pointed out thatfor 100 parts of cellulose nitrate 40 to 50 parts 0 camphor may be used.

By the use of our process, films or sheets may be produced which areclean and readily moldable and yet have all the desirable properties offilms made from cellulose nitrate or pyroxylin having a nitrogen contentof 12% and of normal viscosity. An important application of ourinvention is the formation of comparatively thick films or sheets ofpyroxylin. Heretofore the preparation of sheets or thick films byflowing solutions of the same on polished surfaces has been extremelydiflicult, if not impossible. Because --of the low viscositycharacteristics of the cellulose nitrate employed, the solution of thesame may be cast in such thickness, that the films or sheets resultingfrom the evaporation of the volatile solvent thereof have thicknessesequal to that of the thinner sheets formed by cutting from solid blocksof plastic composition Thus by our process, flowed sheets may be formedthat have a thickn es's of .015 inch gauge-a result that has not beenattainable heretofore.

The sheets or films produced by our process have smooth andhighlypolished surfaces and may be as readil shaped by molding and embosslngas sheets ormed by planing blocks of pastic masses containing cellulosenitrate. Unlike sheets formed by planing, the sheets made by our processare free of ploughed lines, so that even when heat or a solvent is aplied to our films or sheets, the highly g ossed surfaces areunafiected. These sheets or films have a clarityand transparencysuperior to those heretofore made, have a high degree of plasticity, andmay be readily cemented to other surfaces.

purposes for which films have been heretoore used, such as photographicfilms, and

" may also be put to the use to which planed sheets have been put. Animportantapplication of the films or sheets produced by our process isin the making of laminated glass.

We are aware of the fact that varnish films have been formed on metallicor other Because of these properties, they are eminently suited for allsubscribed our s Parts Cellulose nitrate of.11% nitrogen content and 15seconds viscosity 100 Camphor -50, Urea 1 Acetone 00 0 This solution iscarefully filtered to clarify the same and to remove foreign matter. The

solution is flowed on the rim of a slowly rotating large wheel inrequired thicknesses and the acetone is caused to evaporate y exposureto the air. The films or sheets thus produced are stripped from thewheel.

It is to be understood that theforegoing detailed description is givenmerely by way of illustration and that many variations may 'be madetherein'without departing from the spirit of our invention.

Having described our invention what we claim and desire to secure byLetters Patent is: k

'1. Method of preparing films or sheets comprising applying 'a solutioncontaining 'a volatile solvent and cellulose nitrate hav-' ing aviscosity of 10 to 7 5 seconds and a nitrogen content 9f 10.7 to 11.35%vto a surface,'permitting the volatile solvent to evaporate and thenstripping the film or sheet thus formed from the surface.

2. A flowcd sheet or'film containing cellulose nitrate of a viscosity of10 to 75 seconds and having a nitrogen content of 10.7 to

3. A composition of matter ada ted to be applied to a surface in themanu acture of 'films or sheets, containing cellulose nitrate having aviscosity of 10 to 75 seconds and a nitrogen content of 10.7 to 11.35%and a vol- .atile solvent.

In testimony whereof, we have hereunto names.

JAMES F. WALSH. THOMAS E. ALOORN.

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